WO2016096462A1

WO2016096462A1 - Spark plugs with central electrode

Info

Publication number: WO2016096462A1
Application number: PCT/EP2015/078538
Authority: WO
Inventors: Manfred Roeckelein; Andreas Benz
Original assignee: Robert Bosch Gmbh
Priority date: 2014-12-16
Filing date: 2015-12-03
Publication date: 2016-06-23
Also published as: US10250015B2; CN107005029A; EP3235079B1; ES2865177T3; DE102014226107A1; JP2017538270A; JP6753852B2; US20170346260A1; KR20170094230A; EP3235079A1

Abstract

The invention relates to a spark plug (1) having a housing (2), an insulator (3) which is arranged in the housing (2), a central electrode (10) which is arranged in the insulator (3), and a ground electrode (5) which is arranged on the housing (2). The ground electrode (5) and the central electrode (10) are arranged relative to each other such that the ground electrode (5) and the central electrode (10) form an ignition gap, and a central electrode head (4) of the central electrode (10) lies on a seat (3a) formed on an inner face of the insulator (3). The central electrode (10) has an electrode main part (11) and a core (12) which is arranged in the electrode main part (11), said core (12) consisting of a material which has a higher heat conductivity than the material of the electrode main part (11), and the electrode main part (11) has a diameter (d_E) which is not greater than 1.7 mm.

Description

description

Spark plugs with center electrode

State of the art

The invention is based on a spark plug according to the preamble of the independent claim.

Due to the increasing reduction of the installation space in the engine compartment, less space is available for the individual components, such as the spark plug, in the engine compartment and the components in the engine compartment must be reduced in size. Due to the trend of so-called downsizing of components, new ones are emerging

Challenges in the design of the components and the spark plug.

By downsizing the spark plug and its components, the thermal, electrical and mechanical load on the spark plug and its individual increases

Components. At the same time, the spark plug should have the same good ignition reliability and the same long life as previous spark plugs not subject to downsizing.

Disclosure of the invention

An adaptation of the insulator and the center electrode to the new requirements resulting from the downsizing is a challenge. The insulator is the more sensitive component in the spark plug due to its ceramic nature compared to the metallic components in terms of mechanical and electrical loads.

Investigations by the Applicant have shown that, in spark plugs having a housing, an insulator disposed in the housing, a center electrode arranged in the insulator and a ground electrode arranged on the housing, the ground electrode and the center electrode being arranged relative to one another such that the ground electrode and the center electrode form a spark gap form, and wherein the center electrode with a Cartridge head rests on a formed on an inner side of the insulator seat, and wherein the center electrode has an electrode base body and a in the

Electrode body arranged core, wherein the core consists of a material having a higher thermal conductivity than the material of the electrode body, to ensure the mechanical and electrical stability of the insulator should not be less than a minimum wall thickness. It is important to achieve an optimum between the stability and heat dissipation of the insulator on the one hand and the heat dissipation of the spark plug overall and the life of the spark plug on the other. The object of the present invention is to provide a spark plug that can meet the requirements mentioned above.

This object is achieved by the spark plug according to the invention by the characterizing part of claim 1.

Characterized in that the center electrode as an electrode base body with a core of a material having a higher thermal conductivity than the material of

Electrode body is formed and the electrode body a

Diameter of not greater than 1.7 mm, is achieved according to the invention that a spark plug with this center electrode meets the above requirements. The insulator can be formed with a sufficient wall thickness, whereby the

Spark plug can withstand the thermal, mechanical and electrical loads during operation. The center electrode or the electrode main body can have regions of different diameters. The mentioned limits for the diameter of the

Electrode basic body refer in each case to the largest diameter of the

Electrode base body neglecting the electrode head. Of the

Electrode head is formed at the combustion chamber-remote end of the center electrode. In the spark plug, the electrode head rests on a seat formed on the inside of the insulator. The electrode head extends from the seat formed on the inside of the insulator to the end of the center electrode facing away from the combustion chamber. If the geometry of the cross section of the electrode main body deviates from the round shape, then the diameter refers to the circumference of the non-circular

Geometry of the cross section of the electrode main body. In a preferred embodiment, the diameter of the electrode main body is not greater than 1.5 mm.

Further advantageous embodiments are the subject of the dependent claims.

Alternatively or additionally, it may also be provided that the diameter of the

Electrode body is not less than 1 mm, so that the stability of the center electrode itself is not compromised. Preferably, the electrode main body should have this minimum diameter, so that the cross section of the electrode body is large enough for sufficient heat dissipation along the center electrode, so that the insulator at its combustion chamber end next to that from the combustion chamber

absorbed heat not additionally with that of the center electrode

absorbed heat is charged. Ideally, that of the combustion chamber

absorbed heat within the center electrode in the combustion chamber further away and thus passed cooler areas.

The housing and the center electrode are at different electrical

Potentials. In the area of the seat formed on the insulator, the center electrode and the housing have, by design, their smallest distance from each other. As a result, this area of the insulator is very susceptible to electrical breakdown. To prevent these electrical breakdowns on the insulator, it has been found to be advantageous that the insulator in the region of the seat formed on its inside a

Wall thickness of not less than 2 mm. Additionally or alternatively, it can be provided that the region of the insulator surrounding the electrode head has a wall thickness of not less than 2 mm. This ensures that the insulator has a sufficiently large wall thickness in order to withstand the high electrical fields occurring in the region of the seat formed on the insulator and electrical breakdowns caused thereby. Advantageously, the core of the electrode base body consists of a material which has a higher thermal conductivity than the material of the electrode base body. As a result, the heat conduction within the electrode body is favored. The material of the core preferably has a thermal conductivity of at least 350 W / m K at room temperature. Additionally or alternatively, it can be provided that at room temperature, the thermal conductivity of the material of the core is at least 300 W / mK greater than the thermal conductivity of the material of the electrode body. The electrode base body has, for example, a nickel-containing alloy.

The alloy preferably contains at least 20% by weight of chromium, in particular at least 25% by weight of chromium. In an alternative nickel alloy, this contains alternatively or additionally yttrium. The core consists for example of copper or silver or an alloy with copper and / or silver. Investigations by the Applicant have shown that, for example, a copper-containing core in the electrode base body reduces the temperature at the end of the electrode main body facing the combustion chamber by 50-80K.

Further investigations by the Applicant have shown that for sufficiently good heat dissipation, i. a heat reduction within the center electrode, the

Cross sectional area of the core not less than 20% of the cross sectional area of the

Electrode body or the center electrode is in at least a first region, wherein in the at least one first region of the electrode base body and the core each have a constant diameter. The cross-sectional area of the electrode main body is composed of the cross-sectional area of the core and the cross-sectional area of the shell. Preferably, the at least one first region is cylindrical. The at least one first region preferably has a length along the longitudinal axis of the center electrode which is equal to or longer than the diameter of the electrode main body in this first region, in particular the length of the at least one first region is at least 1.5 times as long as the first electrode Diameter of the electrode body.

Additionally or alternatively, it may be provided that the cross-sectional area of the core corresponds to a maximum of 65% of the total cross-sectional area of the electrode main body or of the center electrode. This ensures that the center electrode has a sufficiently large shell thickness.

Advantageously, the electrode base body consists of a more wear-resistant material than the core, so that preferably the electrode base body must have a minimum cladding thickness so that the center electrode has a sufficiently long life, for example at least 50,000 km. It has proved to be advantageous if the electrode main body has a minimum cladding thickness of not less than 0.15 mm, in particular not less than 0.25 mm. Additionally or alternatively, it can be provided that the jacket thickness in the at least one first region with constant diameters of the core and the electrode main body is not greater than 0.35 mm.

In a preferred embodiment of the invention, the center electrode on its combustion chamber-side end face on a precious metal-containing ignition surface, which has a higher wear resistance than the electrode body material. The distance b from the firing surface to the core has a value in the range of 0.2 mm to 2 mm.

In an alternative development of the invention, the center electrode has no

Ignition surface on. In this case, the distance b from the combustion-chamber-side end face of the electrode main body to the combustion-chamber-side end of the core is at least 0.6 mm long in order to ensure a sufficiently long service life of the center electrode. The distance b preferably has a value not smaller than 1 mm, and especially not larger than 3.5 mm.

It is advantageously provided that the cross-sectional area of the core and the

Cross-sectional area of the electrode main body have the same geometric shape, in particular the core within a cross-sectional plane in the middle in

Electrode body is arranged. This ensures that the

Electrode body has a uniform shell thickness within the cross-sectional plane.

Spark plug with a reduced outer diameter of the housing are within the meaning of this application spark plugs whose threads have a smaller outer diameter than 14 mm, for example, so-called M12 or MIO spark plugs.

drawing

FIG. 1 shows two examples of central electrodes

Figure 2 shows a section of the center electrode FIG. 3 shows a spark plug according to the invention with a center electrode

Description of the embodiment

FIG. 1 shows schematic representations for two exemplary embodiments of the center electrode 10. The center electrode 10 has an electrode base body 11 and a core 12 which is arranged inside the electrode base body 12. The core 11 is made of a material having a higher thermal conductivity than the material of the electrode base body 11. Typically, the material of the electrode base body 11 has a higher wear resistance than the material of the core 12. The core 12 is made of copper, silver or an alloy with copper and / or silver. As the material for the electrode main body 11, a Ni alloy is preferably used, while chromium and / or yttrium may be contained in the alloy.

Due to the manufacturing process, here an extrusion process, the core of the center electrode 10 shown here in section has at least a first portion 15a, in which the core 12 has a relatively constant diameter d _K. For the purposes of this application, the term "relatively constant" means that the diameter d _K in the section changes its value by a maximum of 5%.

The diameter d _{K of} the core 12 is reduced within a second section 14a. The at least one first section 15a is arranged on a side of the center electrode 10 facing away from the combustion chamber, wherein an electrode head 4 (not shown) adjoins the end of the first section facing away from the combustion chamber 15 is formed. In the direction of the combustion chamber, the second section 14a adjoins the at least one first section 15a. In principle, it is conceivable for the core 12 to have a plurality of first sections 15a with constant diameters d _K , the diameters d _{K of} the individual first sections 15a being different. This is the case in particular when the center electrode 10 or the electrode main body 11 itself has several

Having regions of different diameters d _E. In the case of a plurality of first portions 15 a of the core, the portion closest to the combustion chamber is the second portion 14 a with the continuously decreasing diameter d _{K of} the core 12. The center electrode 10 shown in FIG. 1 is constructed from an electrode main body 11 which has a constant diameter d _E along its length and thus also the center electrode 10 has a constant diameter d _E. In the electrode main body 11, at least three regions 13, 14, 15 can be distinguished. In a first region 15, the electrode main body 11 has a core 12 with a constant diameter d _K. In a second region 14a, the

Electrode base body 11 a core 12 with a continuously reducing diameter d _K on. In a third region 13, the electrode main body 11 has no core.

The thickness c of the jacket of the electrode base body 11 results from half the difference of the electrode body diameter d _E to the core diameter d _K. When the electrode base body 11 in the first region 15 is a constant

Diameter d _E1 , then the shell thickness c in this first region 15 is constant. It is advantageously provided that in this first region 15, the jacket thickness c of the electrode base body 11 is not less than 0.15 mm and not greater than 0.35 mm, for example, the jacket thickness c is equal to 0.25 mm or smaller.

In the second region 14 of the electrode base body 11 is a constant

Have diameter d _E2 , in which case the shell thickness c within the

Area 14 increases in the direction of the combustion chamber. The jacket thickness c is at least 0.15 mm thick in the region 14.

In an alternative embodiment, not shown here, the diameter d _{E2 of} the electrode base body 11 in the second region 14 can likewise be reduced. In this case, the jacket thickness c is preferably 0.15 mm to 0.35 mm. It can be provided that the diameter d _E2 of

Electrode body 11 changes at the same rate as the diameter d _{K of} the core 12. This has the advantage that the jacket thickness c remains constant in the second region 14.

There is no core in the third region 13 of the electrode main body 11, and thus the jacket thickness c corresponds to half the diameter d _{E3 of} the electrode base body 11. The third region 13 preferably has a constant diameter d _E3 which corresponds to the diameter d _{E2 of} the second region 14 during the transition to the third area 13 corresponds. The third region 13 of the electrode main body 11 has a length b, which extends from a combustion-chamber-side end 17 of the core 12 to a combustion-chamber-side end

End face 16 of the electrode body 11 extends. The length b is not greater than 3.5 mm. If the center electrode 10 is formed with a noble metal-containing ignition surface 19, the length b may be formed shorter than without igniter surface 19 containing noble metal, as shown in Figure lb. If a noble metal-containing ignition surface 19 is dispensed with, as shown in FIG. 1 a, the length b should have a minimum length of 0.6 mm, so that the noble metal base body 12 has enough material for a sufficiently long service life of the center electrode 10. When using a noble metal-containing ignition surface 19 extends a length b of at least 0.2 mm for a sufficiently long life of the center electrode 10th

Figure 2 shows an example of a cross section of the center electrode 10. The diameter d _{E of} the center electrode 10 and the electrode base body 11 is smaller than 1.7 mm. The cross section of the core 12 is arranged centrally in the cross section of the central electrode 10 or of the electrode main body 11. The thickness c of the mantle of the

Electrode base body 11 results from half the difference of

Electrode body diameter d _E to the core diameter d _K.

Advantageously, the cross sections of the electrode main body 11 and the core 12 have the same geometric shape.

Figure 3 shows a schematic representation of a spark plug 1 with a

The spark plug 1 has a metallic housing 2 with a thread for mounting the spark plug 1 in a cylinder head. Furthermore, the housing has a hexagonal section 9, on which a tool for the assembly of the spark plug 1 is set in the cylinder head. Within the

Housing 2, an insulator 3 is arranged. A center electrode 10 and a

Connection bolts 7 are arranged inside the insulator 3 and via a

Resistance element 6 electrically connected.

On the inside of the insulator 3, a seat (3a) is formed, on which the center electrode (10) rests with its center electrode head (4). The insulator (3) has a wall thickness of not less than 2 mm in the region of the seat (3a). The center electrode 10 typically protrudes from the insulator 3 at the combustion chamber end of the spark plug 1. The center electrode has a main body 10 and an ignition surface 19 arranged at the combustion chamber end of the main body. The main body 10 has a core 12 which is surrounded by a jacket 11.

At the combustion chamber end of the housing 2, a ground electrode 5 is arranged. Which forms a spark gap together with the center electrode 10. The ground electrode 5 may be formed as a roof electrode, side electrode or ironing electrode.

Claims

claims

A spark plug (1) comprising a housing (2), an insulator (3) arranged in the housing (2), a center electrode (10) arranged in the insulator (3) and a ground electrode (5) arranged on the housing (2), wherein the ground electrode (5) and the center electrode (10) are arranged to each other so that the ground electrode (5) and the center electrode (10) form a Zündspalt, and wherein the center electrode (10) with a

Electrode head (4) on a formed on an inner side of the insulator (3) seat (3a) rests, and wherein the center electrode (10) has an electrode base body (11) and in the electrode base body (11) arranged core (12), wherein the core (12) is made of a material having a higher thermal conductivity than the material of the

Electrode base body (11), characterized in that the

Electrode base body (11) has a diameter (d _E ) of not greater than 1.7 mm.

2. Spark plug (1) according to claim 1, characterized in that the insulator (3) in the region of the formed on its inner side seat (3a) has a wall thickness of not less than 2 mm.

3. Spark plug (1) according to claim 1 or 2, characterized in that the

Center electrode (10) has at least a first region (15), in which the

Electrode base body (11) and the core (12) each have a constant diameter.

4. Spark plug (1) according to claim 3, characterized in that in the at least one first region (15), the cross-sectional area of the core (12) corresponds to at least 20% of the total cross-sectional area of the electrode (10).

5. Spark plug (1) according to claim 3 or 4, characterized in that in the at least one first region (15), the cross-sectional area of the core (12) corresponds to a maximum of 65% of the total cross-sectional area of the electrode (10).

6. Spark plug (1) according to one of claims 3 to 5, characterized in that the electrode base body (11) has a jacket thickness c of at least 0.15 mm, and

in particular of not more than 0.35 mm, in particular in the at least one first region (15).

7. Spark plug (1) according to one of the preceding claims, characterized in that at a combustion chamber end (16) of the electrode base body (11) of the distance b between the end (16) of the electrode base body (11) and a combustion chamber facing the end (17 ) of the core (12) is not greater than 3.5 mm, and in particular not less than 0.2 mm.

8. Spark plug (1) according to one of claims 3 to 7, characterized in that the at least one first region (15) longer than the diameter of the

Electrode base body (11).

9. spark plug (1) according to one of the preceding claims, characterized in that the cross-sectional area of the core (12) and the cross-sectional area of the

Electrode main body (11) have the same shape.

10. Spark plug (1) according to one of the preceding claims, characterized in that the electrode base body (11) comprises a nickel-containing alloy, in particular that the alloy has at least 20 wt.% Chromium.